It's amazing how quickly things change in the scouting world when it comes to evaluating prospects.

Players see their draft stock fluctuate up and down like a roller coaster based on performances at postseason bowl games, the NFL Scouting Combine and pro days. In addition, the extensive evaluation of game tape, background profiles and medical history impact a player's final standing on the draft board.

Just take a look at Dontari Poe and his fortunes since the end of the regular season. The former Memphis defensive tackle was widely viewed as a bottom-of-the-first-round talent based on pure game tape. Scouts saw him as a player with the ability to improve a roster as a situational starter in his rookie season.

However, that perception changed after his impressive display of speed, strength and athleticism at the combine.

At 6-foot-3, 346 pounds, Poe clocked a 4.98 in the 40, led all participants with 44 reps on the bench press and displayed remarkable athleticism and movement skills for a man of his size. From flowing effortlessly through bag drills to showing the ability to bend the corner on pass-rush drills, Poe looked like a "can't-miss" prospect with the tools to become a real difference maker as a pro. Coaches and scouts lauded his ability, with most expecting him to come off the board within the top 10.

In recent weeks, though, the tide has turned again as evaluators have taken more time to pore over his tape. Scouts have cited concerns about his lack of production and impact against lightly regarded competition. Poe finished his three-year career with only five sacks, including just one in 2011, and wasn't recognized by his peers or coaches as one of the most dominant defenders in Conference USA. (Poe twice earned Honorable Mention status on the conference's all-league teams during his career.)

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While I certainly understand the growing concern, let's not forget about Poe's blue-chip qualities (size, athleticism and strength) and the immense importance of the position. There is no one in this year's draft class that rivals his pure talent at the position. Given those factors, I believe Poe will be the first defensive tackle to come off the board on draft day, despite the question marks surrounding his game.

Here are five other prospects who are making the evaluation process difficult for scouts and coaches:

Brock Osweiler, QB, Arizona State: The 6-foot-7 gunslinger created a buzz in scouting circles with his strong performance at Arizona State's pro day, but many evaluators are still uncertain about his pro potential. He enters the league with only 15 collegiate starts and his quirky side-arm delivery is troubling to some quarterback coaches. Furthermore, his enormous stature leads to concerns about his ability to escape rushers in the pocket. While the upside and potential is apparent on the tape, some red flags could keep Osweiler from hearing his name called early in the draft.

Mike Adams, OT, Ohio State: Adams might be the most gifted offensive tackle in the draft, but his inconsistent play will likely prevent him from being drafted in a slot that reflects his raw talent. He fails to consistently dominate elite rushers, despite possessing the length and movement skills to win isolated matchups. His failures are routinely attributed to mental lapses, raising concerns about his focus and concentration. With his maturity already in question due to a series of off-field incidents, Adams' high draft status remains in jeopardy.

Rueben Randle, WR, LSU: After posting disappointing times at the combine, Randle made amends with a strong showing at LSU's pro day. He clocked 40 times in the high-4.3 range and displayed exceptional hands and route-running ability. Randle's impressive performance in front of scouts has prompted decision makers to review his game tape to see if he has the goods to be a No. 1 receiver at the next level. While his collegiate production would suggest otherwise, Randle could be a surprise early selection on draft day.

Dwayne Allen, TE, Clemson: Allen was anointed as the top tight end prospect heading into the NFL Scouting Combine, given his exceptional production at Clemson. Teams pegged him as a matchup nightmare with his size and athleticism, but a disappointing 40 time (4.89) in Indianapolis has altered that perception in some draft rooms. However, scouts conducting their due diligence on Allen's game tapes are intrigued by his ability to consistently get open against an array of coverages. Given the increased role of tight ends in most offenses, the final assessment of Allen's potential to impact the passing game as a deep-middle threat will decide his fate as a potential top-50 selection.

Nick Perry, DE, USC: The proliferation of the passing game has prompted teams to search high and low for defensive ends with rush skills. Perry is squarely on the radar based on his solid production during his final season at USC and an impressive showing at the combine. But scouts are still struggling with his final grade due to the extended lulls in his play and a lack of pizzazz as a pass rusher. While Perry certainly flashes potential to wreak havoc off the edge, he isn't a lock to come off the board in the first round.